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Introduction

Water is the basis of existence of all life forms in our biosphere. Of all the planet’s renewable resources, water has a unique place. It is essential for sustaining all forms of life, food production, economic development and for general well being. Accelerated urbanization and industrialization has made water bodies susceptible to various threats. Aquatic ecosystem is exposed to local disturbances, Suryanaraynan (1991). According to Laalet al.(1986) and Nath (2001), thorough knowledge of physico-chemical conditions prevailing in a water body is important for the assessment of water quality and extent of pollution. Prevailing physicochemical characteristics of water regulates the population dynamic and distribution of the inhabiting zooplanktons. A knowledge of both the organism and its environment is, therefore, very essential and pre-requisite for understanding the various life history parameters of aquatic organisms, Weltch (1952).

Zooplanktons serve as an important link in the food chain of an aquatic environment. They constitute a major portion of diet of fishes and play a very important role in nutrition particularly when developing young fish switches from endogenous to exogenous mode of feeding. Live feeds are additionally superior to compounded ones, because they are readily ingested and digested rapidly do not affect water quality, besides, having essential inherent growth promoting factors, Kinne (1977) and Watanabeet al., (1983).

Apart from serving as important fish food organism, zooplanktons are considered as indicators of water quality. The distribution and abundance of these organisms in polluted and unpolluted water can provide useful information on the health of the water body, Gajbhiyeet al., (1981).

It was with this background that present work was undertaken to analyze the physico-chemical parameters, seasonal abundance of zooplankton and the relationship between the former and latter.

Table 1: Monthly variations in Physico-Chemical Parameters of a Pond of Jammu Click here to view table

Material and Methods

研究区,Janipur池塘Ja以西十公里mmu (old) city. The pond is spring fed, covers 0.023 Sq. kilometer surface area and has mean depth of 1 meter samples were collected from three study stations raised along the periphery. Station-I (S-I) located along the margin of the road and is void of vegetation. Station-II (S-II) is characterized by dense vegetation and is mainly used by cattles for drinking and bathing. Station-III (S-III) receives water from catchment area.

Temperature was recorded with the help of a thermometermeter graduated up to 100^oC. pH of the water was determined by a field pH meter (Hanna instruments Italy). Dissolved oxygen, Free carbon dioxide, Carbonates, Bicarbonates, Calcium, Magnesium and Chlorides were estimated by applying method suggested by Indian standard methods (1973) and APHA (1985). Analysis of zooplankton was carried following Edmondson, (1959) and Needham and Needham (1962).

Table 2 : Monthly variations in Physico-Chemical Parameters of a Pond of Jammu Click here to view table

Results and Discussion

Monthly variations in various physico-chemical factors are shown in Table-I. Air temperature ranged from minima of 18^oC in the month of January to maxima of 39^oC in May. Water temperature showed a corresponding variation and fluctuated from a minimum of 17^oC in January to a maximum of 34^oC in August. The water temperature closely followed air temperature as earlier advocated by Qadri and Yousuf (1980), Rainaet al．(1982),辛格和辛格(1995),Panday和拉尔(1995), Sharma (2001), Shafiq (2004), Sawhney (2004) and Shvetambri (2007). The rise in temperature (Air and Water) is primarily due to increased day length (Summer 14 hours and winter 10 hours) and sharp angle of incidence during summers. pH of the water remained mostly alkaline except for the months of June (6.8) and September (6.1). pH was low, when Free CO₂and HCO₃in the water-body were quite high (Table-I) and therefore were major contributing factors towards acidic nature of water during the period of study. Similar observations were made by Lalet al．(1986) and Charkrabortyet al．(1995). A fall in pH was observed in monsoon and was attributed to CO₃^2-and increased Free CO₂．This has been supported by Qadri and Yousuf (1980) who maintained that the rain water and associated decaying organic matter inundating into the waterbody are responsible for such a change in pH. Dissolved oxygen of the pond fluctuated from a minima of 3.6 mg/l (August 2004) to a maxima of 15.2 mg/l (November 2004). The rise and fall in temperature was responsible for an increase and decrease in the DO content respectively and also affected the photosynthetic activities of Chlorophyll bearing organisms. The results presented in this study are in accordance with result of earlier workers, Sarwar and Parveen (1995), Joshi and Singh (1997) and Masudet al．, (2002). Low DO during post monsoon period was probably due to the turbidity and waste material entering into water body along with rainwater. Higher value of DO during winter and low during post monsoon is a well-known characteristics feature of stable aquatic ecosystem as has already been observed by many workers , Lalet al,(1986)。每月的变化自由有限公司₂is shown in Table-I. Higher values of Free CO₂during post monsoon months corroborate with the finding of Laalet al.(1986). An increase in Free CO₂during post monsoon months is broadly attributed to added load of decayed organic matter brought by rainwater. Absence of Free CO₂during November and December at all the three stations may be being of its uptake by phytoplankton and submerged rooted vegetation. Monthly variation in Carbonate (CO₃^2-) and Bicarbonate (HCO^3-) are shown in Table -I. Absence of carbonate (CO₃^2-在大多数的mon)ths may explain the presence of Free carbon dioxide. An inverse relationship between carbonates and Free CO₂has been advocated by Goldman and Horne (1983), Singh (1995) and Sharma (1999).

Table 3 : Monthly variations in Zooplankton abundance of a pond of Jammu Click here to view table

The value of bicarbonate increased during summer months and decreased during winter. The rainfall plays a significant role in increasing the concentration of bicarbonate.

Calcium (Ca⁺⁺) and Magnesium (Mg⁺⁺) also showed well-marked seasonal variation throughout the investigated period. Higher values of Ca⁺⁺at station-II might be due to the allochthonous material especially the excretory wastes of cattles, which October. This complete absence of cladocerans may be attributed to high temperature. Among Cladocerans,Daphniadominated (2982/l). Cladocerans were mostly present during the moderate temperature range (17-20^oC) as documented by Saint-Jean (1983) who reported that cooler periods favour the cladoceran dominance. Rotifer production exhibited an inverse correlation with DO and free CO₂．During the present investigation DO was recorded to be highest 15.2 mg/lt in November whenMoinashowed its presence. This species was also present in the month of August (15/l) at lowest DO level, revealing its wide tolerance for oxygen variation. Other cladocerans were more or less absent during the months of low DO level. Maximum qualitative abundance of cladocerans was recorded during the month of December, January and February which was probably due to the combined effect of favourable temperature, high Ca⁺⁺, Mg⁺⁺and optimum pH of water. From above discussion it appear that zooplankton population showed two peaks, 1^stduring January and February which was exclusively due toDaphniaspecies. During this period temperature was low (17^oC and 19^oC) and DO was high (8.8 and 9.2 mg/l). February onwards, water temperature observed a gradual increase (19^oC-34^oC) and this resulted in sudden disappearance ofDaphniaand zooplankton fauna was exclusively dominated by rotifers. After March till July, zooplankton fauna was characterized by high free CO₂, low level of Ca⁺⁺and Mg⁺⁺, high temperature condition (upto 34^oC in May at S-III). Prevalence of copepods as a dominant group during the presently studied period strongly indicates copepods to be better tolerant of temperature as compared to rotifers and cladocerans.

Acknowledgements

The authors are thankful to the Head, Deptt. Of Zoology for providing necessary laboratory facilities.

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